1. Field of the Invention
The present invention relates to a picture coding and decoding technology, and more particularly, to a technology for entropy coding and decoding of a residual signal.
2. Description of the Related Art
In MPEG-4 AVC that is an international standard of moving picture coding, as an entropy coding system, context switching-type arithmetic coding called CABAC is employed. CABAC includes a plurality of variables called a context that stores the occurrence probability of information to be coded. An optimal context is selected from among neighboring coding information and is used for coding. In addition, since the occurrence probability is updated according to a coding process also in each context, the occurrence probability of coding information can be estimated with high accuracy, whereby efficient coding can be performed.    Patent Literature 1: JP 2007-300517 A
In the MPEG-4 AVC, in addition to the estimation of the occurrence probability of information according to switching a context based on the neighboring decoded information, the occurrence probability according to a decoding result is learned. The occurrence probability of information to be decoded can be optimized for each context, and accordingly, the improvement of the coding efficiency is realized. However, for all the significant differential coefficient information within the block to be processed, it is necessary to sequentially process the calculation of context indexes and decoding of the significant differential coefficient information, and a calculation time is required.
In Patent Literature 1, a technique for decreasing a processing delay relating to decoding is disclosed by arranging a context for a syntax element having a high occurrence frequency on a memory having a small access delay time. However, the technique disclosed in Patent Literature 1, does not resolve the dependency between the calculation of the context index and the decoding of a syntax element, and these processes cannot be performed in a parallel manner and is not an essential solution for a processing delay.